Cylinder with two concentric pistons actuated by a pressure medium and extending to three times the length of the cylinder

ABSTRACT

The invention concerns a cylinder-piston combination actuated by a pressure medium, comprising an outstretched cylinder space (1) and a two-part piston assembly (3, 8) movable in opposite directions in the longitudinal direction of the cylinder space (1). The piston rod (6) of the first part (3) of the piston assembly is of a tubular construction. The first part (3) is provided with a sealing between the piston (4) and the inner surface (2) of the cylinder space (1). The cylinder space (1) is provided with a connection (27) through which the pressure medium can be passed into the space (31) limited by the cylinder space (1) and the outer surface of the first part (3). The second part (8) is constructed to dimensions allowing it to fit inside the first part (3) and arranged to be movable relative to the latter. The combination includes an auxiliary piston (14) fitted around the piston rod (13) of the second part and sealed relative to the inner surface (2) of the cylinder space (1). The cylinder space is provided with a connection (25) permitting the passage of the pressure medium into the space (29) limited by the cylinder space (1) and the auxiliary piston end face (20) facing away from the first part (3). The cylinder space (1) is provided with another connection (26) permitting the passage of the pressure medium to the auxiliary piston end face (21) facing towards the first part (3) when the piston (9) of the second part (8) is in engagement with the auxiliary piston (14).

FIELD OF THE INVENTION

The present invention relates to a cylinder-piston combination actuatedby a pressure medium. The combination has an out-stretched cylinderspace and a two-part piston assembly so arranged that it will move inopposite directions in the axial direction of the cylinder space.

BACKGROUND OF THE INVENTION

In previously used solutions in this category, the pistons in the pistonassembly are placed inside the cylinder space opposite to each other,with the piston rods protruding from opposite ends of the cylinder, thelength of each rod equalling essentially half the length of the cylinderspace Thus the maximum length of the combination is essentially twicethat of the cylinder space. In many cases, this is not sufficient inview of the required change in the length, especially when the spaceavailable imposes restrictions on the maximum length and otherdimensions of the cylinder space. Such a situation prevails especiallyin telescopic boom structures which should be extendable to a sufficientlength when working and still be able to contract into a sufficientlycompact form when at rest.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a cylinder-pistoncombination which is extendable to a length essentially three times thatof the cylinder space. None of the external dimensions of thecombination differs substantially from the corresponding dimension of aconventional dual-piston cylinder. The combination has a simplestructure and its control functions are easy to implement using normalcontrol techniques.

The chief characteristics of the invention are as exposed in claim 1.Certain preferred embodiments are presented in the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described with reference to thedrawings attached. FIGS. 1-3 are longitudinal sectional views of one ofthe possible implementations in different phases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 represents the cylinder-piston combination with the piston rodsinside the cylinder, the combination being contracted to its minimumlength The cylinder space 1 is constituted by a jacket tube 1a,preferably of a round sectional form. The first part 3 of the pistonassembly--via the mediation of the outer piston 4 belonging to it--is incontact with the inside surface 2 of the jacket tube. The outer piston 4is provided with sealings 5 between the piston and the inside surface 2.When the combination opens, the piston rod 6 of the first part 3 in FIG.1 moves right and is pushed against the seal 7 belonging to theright-hand end flange 1b of the cylinder space 1. The piston rod 6 is ofa tubular construction and its inner diameter corresponds to thediameter of the inner piston 9 belonging to the second part 8 of thepiston assembly. In the closed position of the combination, the secondpart 8 is substantially inside the first part 3. The outer surface ofthe inner piston 9 is provided with several axial grooves 10. When thecombination opens, the piston rod 13 of the second part 8 in FIG. 1moves left and is pushed against the sealing 12 belonging to theleft-hand end flange 1c of the cylinder space 1. The piston rod 13 maybe either tubular, as in the present example, or a solid rod.

The combination also comprises an auxiliary piston 14, with sealings 15between the piston and the inside surface 2 of the cylinder space 1. Theauxiliary piston 14 is provided with a central opening 16 to allow thepiston rod 13 of the second part 8 to move relative to the auxiliarypiston 14. In addition, the auxiliary piston has a cut-out 17 whosedimensions essentially correspond to those of the inner piston 9, andone or more projections 18 and 19 or equivalent, preferably located onthe end faces 20 and 21. The auxiliary piston 14 is also provided with asealing 23 to seal the gap between itself and the piston rod 13. At thepoint of connection between the outer piston 4 and the piston rod 6 is ashoulder 24.

The jacket tube 1a of the cylinder space 1 is provided with threeconnections 25, 26, 27 through which the pressure medium is passed intothe cylinder space 1 to control the operation of the combination.

Through the first connection 25, a pressure is applied to the left-handend face 20 of the auxiliary piston, i.e. the medium is passed into thespace 29 formed between the end flange 1c and the auxiliary piston 14 bymeans of the projection 18 when the combination is in the closedposition as shown in FIG. 1. Through the second connection 26, withouter piston 4 positioned to the right as shown in FIG. 2, a pressure isapplied to the portion 30 of the cylinder space limited by the insidesurface of the outer piston 4, the end face 21 of the auxiliary piston14 and the outer surface of the second part 8. Through the thirdconnection 27, a pressure is applied to the cylinder space portion 31limited by the outer surface of the first part 3. The space 32 betweenthe end 28 of the piston rod 6 and the inner piston 9 also plays a rolein the transfer of the pressure medium. The connections for the pressuremedium are so located that, during a cycle of operation of thecombination, each is active in turn.

Referring to the drawings, the combination works as follows:

When the pressure medium is allowed to flow from the first connection 25into the space 29, the combination will move from the closed positionshown in FIG. 1, in which the inner piston is inside the piston rod 6 atthe right-hand end of the cylinder space and the outer piston 4 as wellas the auxiliary piston are at the left-hand end of the cylinder spaceat a distance determined by the shoulder 19 from each other, into theposition shown in FIG. 2. The auxiliary piston 14 pushes the first part3 to the right-hand end of the cylinder space, so that the piston rod 6moves out of the cylinder space 1 until the shoulder 24 is pressedagainst the end flange 1b and the space 31 is at a minimum. During thismovement, the connection 27, and possibly connection 26 as well, is opento permit the pressure medium to flow out of the space 31 The space 30is also reduced during this movement and the pressure medium in it flowsthrough holes 10 into the space 32. Holes 40 penetrating in the axialdirection of piston 9 can be provided. At the end of the movement, theinner piston 9 is in the cut-out 17 in the auxiliary piston 14 as shownin FIG. 2, so that the spaces 30 and 32 shown in FIG. 2 merge and theconnection 26 is to the right of the auxiliary piston end face 21 andcan therefore communicate with the spaces 30 and 32. FIG. 4 shows asection IV--IV through the combination. The connection 27 communicateswith the space 31.

When the pressure medium is allowed to flow via the connection 26 intothe spaces 30 and 32, the combination of the inner piston 9 and theauxiliary piston 14 moves left to the position shown in FIG. 3 as thepressure acts on the end face 21,34 formed by the two pistons together,and the piston rod 13 moves simultaneously to its outermost position onthe left. During this movement, the connection 25 has to be open toallow the pressure medium in the diminishing space 29 to flow out. Thecombination is now extended to its maximum length, essentially threetimes the length of the cylinder space. With the aid of the auxiliarypiston 14, the piston rods 6 and 13 have been successively forced outfrom the cylinder space.

When the combination is to be brought again into the position shown inFIG. 1, the pressure medium is first allowed to flow from the connection25 into the space 29 while the connection 27 is kept open. As a result,the combination moves into the position shown in FIG. 2. Next, thepressure medium is caused to flow via connection 27 into the space 31while connection 25 is kept open and connection 26 closed, resulting inthe situation shown in FIG. 1. Now, with the inner piston 9 remaining inplace, separate spaces 30 and 32 are restored. This function can beimplemented by providing the cylinder jacket 1a with an additionalconnection 35 located to the right of the end face 21 when the auxiliarypiston is in its extreme position on the left (FIG. 1). Thus the portionof the pressure medium which is stored between the auxiliary piston 14and the first part 3 and which increases the distance between themduring the right-to-left movement, the volume of said portioncorresponding to the capacity of the piston rod 3, is exhausted via theadditional connection 35 when the auxiliary piston 14 reaches itsleft-hand extreme position, allowing the additional connection 35 tocommunicate with the space 30. The system also comprises a pressurecylinder 36 actuated by the pressure medium, enabling the piston rod 13to be locked in its inner position when the piston rod 6 is brought toits inner position.

Obviously the invention can be implemented in other ways besides thosedescribed above. It is possible that the cut-out 17 in the auxiliarypiston 14 is unnecessary in some embodiments. The shoulder arrangementsused to achieve the minima of the pressure spaces may be implemented indifferent ways. The pressure medium is preferably hydraulic oil. Clearlyit is possible to implement the closing of the combination in thereverse order compared to that described in the example. The orderdescribed is especially suited for applications employing the telescopicextension principle. The control of the operation of the connections canbe implemented e.g. using magnetic valves in the lines connected tothem.

I claim:
 1. Cylinder-piston combination actuated by a pressure medium, comprising an outstretched cylinder space (1) and a two-part piston assembly (3, 8) movable in opposite directions in the axial direction of the cylinder space (1), the piston rod (6) of the first part (3) of the piston assembly having a tubular construction, the first part (3) being provided with a sealing between the piston (4) and the inner surface (2) of the cylinder space (1), the cylinder space (1) being provided with a connection (27) through which the pressure medium can be passed into the space (31) limited by the cylinder space (1) and the outer surface of the first part (3), the second part (8) being constructed to dimensions allowing it to fit inside the first part (3) and arranged to be movable relative to the latter, characterized in that the combination comprises an auxiliary piston (14) fitted around the piston rod (13) of the second part and sealed relative to the inner surface (2) of the cylinder space (1), that the cylinder space is provided with a connection (25) permitting the passage of the pressure medium into the space (29) limited by he cylinder space (1) and the auxiliary piston end face (20) facing away from the first part (3), and that the cylinder space (1) is provided with another connection (26) permitting the passage of the pressure medium to the auxiliary piston end face (21) facing towards the first part (3) when the piston (9) of the second part (8) is in engagement with the auxiliary piston (14).
 2. Combination according to claim 1, characterized in that the first part (3) is provided with a shoulder (24).
 3. Combination according to claim 1, characterized in that the piston rod (6) of the first part (3) has a solid end (28), so that a space (32) for the pressure medium is formed between the inside of the piston rod (6) and the piston (9) of the second part (8).
 4. Combination according to claim 1 or 3, wherein the piston (a) is provided with at least one hole penetrating it in the axial direction.
 5. Combination according to claim 1, characterized in that the auxiliary piston is provided with a cut-out for the piston (9).
 6. Combination according to claim 1, characterized in that the auxiliary piston (14) is provided with distance pieces (18, 19) preferably projecting from its end faces (20, 21).
 7. Combination according to claim 1, characterized in that the cylinder space (1) is provided with an additional connection (35) which, relative to the auxiliary piston (14), is located opposite to the space (29).
 8. Combination according to claims 1 or 3 wherein the piston (9) is provided with at least one groove 10 on its outer shell.
 9. Combination according to claim 4 wherein the piston (9) is provided with at least one groove on its outer shell. 